The invention relates broadly to the object measuring art, and more specifically to the art concerned with on line measurement and instant determination of physical parameters by non-contacting means.
Hot rolling of steel ingots into strips is traditionally divided into at least four processes. Slabbing ingots (as cast) are first handled in a blooming and slabbing mill, to emerge typically as twenty foot long, four to eight inch thick sections. Roughing stands reduce thickness further to (typically) three quarters of an inch. In the finishing train, the steel sheet reaches its final thickness and is then water cooled and coiled.
In rolling, a complex relationship exists between composition, temperature, speed, thickness reduction per pass and resulting strip width. Oversize results in increased tonnage without monetary benefits and undersize results in scrap at the coilers. To avoid such losses, it is desirable to monitor directly or indirectly all process parameters and to make the data available to upstream and downstream work stations for on line process corrections.
As with steel strips, float glass plants have similar requirements to monitor both width and edge position and although the consequences may not result in similar losses, product output and good quality are associated with accurate real time dimensional data. Because of high temperatures and line speeds, on line width measurement of float glass at the softened stage and strip steel in the finishing train are particularly difficult. Only reliable, non-contacting methods with fast response times are suitable.
The problems associated with conventional and antiquated methods of hot-strip width measurement deal with moving mechanisms and traversing optical sensors. These may include totally analog technology which is plagued with drift and the necessity for frequent recalibration. A still greater problem, however, is that because the temperature of the hot material may vary, not only along the length but even across the width of the material, the level of illumination reaching the sensors may vary causing a miscalculation in the observed dimension of the hot material. For example, the edge portions of the hot material are typically colder than the midwith portion and thus may not be accurately sensed by the photo detectors.
One prior art system atempted to overcome this problem by providing a mechanical aperture control for one of the photo detectors. See, for example, U.S. Pat. No. 2,931,917. Unfortunately, analog exposure control is far too slow and inaccurate for modern process technology. Another prior art system attempted to overcome the basic slowness of analog measuring systems by providing electronically scanned photo detectors. See, for example, U.S. Pat. No. 3,736,063. This electronically scanned system, however, did not make any provision for varying the exposure of the photo detector to compensate for variations in the temperature of the material. With such electronically scanned photo detectors, the exposure is a product of the intensity of the lumination and the exposure time on the photo detectors. Such devices have exposure ranges which may, for example, be suitable for sensing the presence or absence of the hot material but may be unsuitable for also accurately sensing the edge position of the hot material. What is required is a way to automatically vary the exposure range swiftly so that both tasks may be performed with high accuracy.